Experiment
A 2-tiered approach was used to identify QTLs associated with basal locomotor activity in rodents, as measured by distance traveled in an open field test during a 20 minute time interval. First, 25 BXD recombinant inbred (RI) strains were typed for 400 polymorphic markers at an average spacing of 4 cM to identify potential QTLs (B = C57BL/6J, D = DBA/2J). Second, potential QTLs were confirmed by screening approximately 500 animals from a (C57BL/6J x DBA/2J)F2 intercross. Parental strain C57BL/6J exhibits more activity compared to parental strain DBA/2J. A locus on mouse chromosome 1, Actd1, was significantly associated with locomotor activity in both the RI strains and (C57BL/6J x DBA/2J)F2 intercross. Actd1 maps to approximately 65 cM (LOD=10.5) on mouse Chromosome 1 with a QTL range of 40 cM - 90 cM. QTLs on mouse chromosome 5, Actd2 at 9 cM (P<0.001 at D5Mit72) and Actd3 at 61 cM (P<5 x 0.0001 at D5Mit278), were identified and confirmed, and a QTL on mouse Chromosome 9, Actd4 at 28 cM (P<2 x 0.0001 at D9Mit94), was identified and confirmed. C57BL/6J-derived alleles increase locomotor activity at Actd1, Actd2, and Actd3, while DBA/2J-derived alleles increase locomotor activity at Actd4.
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